Anonymous functions in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an anonymous function that adds 5 to its input.

R Programming

add_five <- function(x) [1] x + 5
add_five(10)

Drag options to blanks, or click blank then click option'

Afunction(x)

Bfunction()

Cfunction(y)

Dfunction(x, y)

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function without parameters like function()

Using a different parameter name than x

The anonymous function must take one argument x and add 5 to it.

2fill in blank

medium

Complete the code to apply an anonymous function that squares each element in the vector.

R Programming

squared <- sapply(c(1, 2, 3), [1](x) x^2)
squared

Drag options to blanks, or click blank then click option'

Afunction()

Bfunction(x)

Cfunction(y)

Dfunction(z)

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function without parameters

Using a parameter name not matching the function argument

The anonymous function must take one argument x and return its square.

3fill in blank

hard

Fix the error in the anonymous function that multiplies input by 3.

R Programming

triple <- [1](x) x * 3
triple(4)

Drag options to blanks, or click blank then click option'

Afunction x

Bfunc(x)

Cfunction(x)

Dfun(x)

Attempts:

3 left

💡 Hint

Common Mistakes

Missing parentheses after function keyword

Using incorrect keywords like func or fun

The correct syntax to define an anonymous function is function(x).

4fill in blank

hard

Fill both blanks to create an anonymous function that returns TRUE if input is greater than 10.

R Programming

check_gt_10 <- [1](x) x [2] 10
check_gt_10(15)

Drag options to blanks, or click blank then click option'

Afunction

Bif

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using if instead of function to define the function

Using the wrong comparison operator

The function keyword defines the anonymous function, and the operator > checks if x is greater than 10.

5fill in blank

hard

Fill all three blanks to create a list of squares for numbers greater than 3 using an anonymous function.

R Programming

result <- lapply(1:5, [1](num) if (num [2] 3) [3] num^2 else NULL)
result

Drag options to blanks, or click blank then click option'

Afunction

B>

Creturn

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using if instead of function to define the function

Using < instead of > for comparison

Omitting the return keyword

The anonymous function is defined with function, uses > to check if the number is greater than 3, and return to output the square.

Practice

1. What is an anonymous function in R?

easy

A. A function that must be saved to a variable

B. A function that always returns NULL

C. A function without a name, created on the spot

D. A function that can only be used once

Solution

1. Step 1: Understand the definition of anonymous functions

   Anonymous functions are functions created without giving them a name, used immediately.

2. Step 2: Compare options with the definition

   Only 'A function without a name, created on the spot' correctly describes an anonymous function.

3. Final Answer:

   A function without a name, created on the spot -> Option C

4. Quick Check:

   Anonymous function = unnamed function [OK]

Hint: Anonymous means no name, created instantly [OK]

Common Mistakes:

• Thinking anonymous functions must be saved to variables
• Believing anonymous functions always return NULL
• Confusing anonymous functions with one-time use functions

2. Which of the following is the correct syntax for an anonymous function in R?

easy

A. lambda x: x + 1

B. fun(x) { return x + 1 }

C. def(x) x + 1

D. function(x) x + 1

Solution

1. Step 1: Recall R syntax for anonymous functions

   In R, anonymous functions are written as function(arguments) expression.

2. Step 2: Check each option

   function(x) x + 1 matches R syntax. Options B, C, and D use syntax from other languages or incorrect forms.

3. Final Answer:

   function(x) x + 1 -> Option D

4. Quick Check:

   R anonymous function syntax = function(args) expr [OK]

Hint: R uses 'function' keyword for anonymous functions [OK]

Common Mistakes:

• Using 'def' or 'lambda' which are Python keywords
• Writing function name instead of 'function'
• Adding unnecessary return statements inside anonymous functions

3. What is the output of this R code?

lapply(1:3, function(x) x * 2)

medium

A. [[1]] 2 [[2]] 4 [[3]] 6

B. [1] 2 4 6

C. [1] 1 2 3

D. Error: object 'x' not found

Solution

1. Step 1: Understand lapply with anonymous function

   lapply applies the function to each element of 1:3, returning a list of results.

2. Step 2: Calculate each element

   For x=1,2,3, function(x) x*2 returns 2,4,6 respectively, stored as list elements.

3. Final Answer:

   [[1]] 2 [[2]] 4 [[3]] 6 -> Option A

4. Quick Check:

   lapply returns list of doubled values [OK]

Hint: lapply returns a list, not a vector [OK]

Common Mistakes:

• Expecting a vector output instead of a list
• Confusing lapply with sapply output
• Thinking anonymous function causes error

4. Identify the error in this R code using an anonymous function:

result <- lapply(1:3, function(x) { x + })

medium

A. Anonymous functions cannot be used inside lapply

B. Missing value after '+' operator

C. Incorrect use of curly braces

D. Variable 'result' is not defined

Solution

1. Step 1: Analyze the anonymous function body

   The function body has 'x +', which is incomplete because '+' needs a value after it.

2. Step 2: Identify the syntax error

   This causes a syntax error due to missing operand after '+'. Other options are incorrect because anonymous functions are valid in lapply, curly braces are correctly used, and 'result' is defined.

3. Final Answer:

   Missing value after '+' operator -> Option B

4. Quick Check:

   Incomplete operator usage = syntax error [OK]

Hint: Check operators have both operands [OK]

Common Mistakes:

• Assuming anonymous functions can't be used in lapply
• Ignoring incomplete expressions inside function
• Confusing variable definition errors with syntax errors

5. How can you use an anonymous function to filter even numbers from a vector v <- 1:6 using Filter() in R?

hard

A. Filter(function(x) x %% 2 == 0, v)

B. Filter(function(x) x / 2 == 0, v)

C. Filter(function(x) x %% 2 = 0, v)

D. Filter(function(x) x == 0, v)

Solution

1. Step 1: Understand filtering even numbers

   Even numbers have zero remainder when divided by 2, so condition is x %% 2 == 0.

2. Step 2: Check each option's condition

   Filter(function(x) x %% 2 == 0, v) correctly uses 'x %% 2 == 0'. Filter(function(x) x / 2 == 0, v) uses division instead of modulo, Filter(function(x) x %% 2 = 0, v) uses single '=', which is assignment not comparison, and Filter(function(x) x == 0, v) checks if x equals zero only.

3. Final Answer:

   Filter(function(x) x %% 2 == 0, v) -> Option A

4. Quick Check:

   Modulo equals zero filters even numbers [OK]

Hint: Use '%% 2 == 0' to check even numbers [OK]

Common Mistakes:

• Using single '=' instead of '==' for comparison
• Using division '/' instead of modulo '%%'
• Filtering for x == 0 instead of even numbers